Frequency-dependent electrical response of holes in poly(p-phenylene vinylene) (original) (raw)
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Hole Transport in Poly(p-Phenylene Vinylene)
physica status solidi (b), 2000
The influence of side chains on hole transport in poly(p-phenylene vinylene) is examined as a function of temperature T and electrical field E by means of current±voltage experiments, and impedance spectroscopy which probes the transit time of injected carriers. The data are analyzed using a model for hopping in a Gaussian site-energy distribution. Energetic disorder predominantly governs the conductive properties of the PPV derivatives.
Comparative study of hole transport in poly(p-phenylene vinylene) derivatives
Physical Review B, 2000
The dc mobility of holes in four poly(p-phenylene vinylene) (PPV) derivatives (three fully conjugated polymers with different side chains and one partially conjugated PPV) is examined as a function of temperature T and applied electrical field E. In all cases the mobility μ follows the ...
Thin Solid Films, 2007
The transport properties (conductivity and mobility) of holes and electrons in poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) light-emitting diodes were investigated using direct current-voltage curves (I-V) and time of flight measurements (TOF) as a function of electric field and temperature. TOF results revealed that the transport of holes in the bulk follows a non-dispersive behavior at room temperature (300 K), exhibiting a progressive transition to a dispersive behavior as the temperature decreases down to 220 K. The dispersive transport characteristics were interpreted in the framework of carrier hopping in an exponential density of states. On the other hand, the analysis of the negative photocurrent transients indicated that the transport of negative charge carriers (electrons) is strongly dominated by trapping in the entire range of temperature studied. The I-V curves presented remarkable temperature dependence, being analyzed in terms of the classic Fowler-Nordheim tunneling, Richardson-Schottky thermionic emission and trap-controlled transport.
Charge transport in poly (p-phenylene vinylene) at low temperature and high electric field
Charge transport in poly(2-methoxy, 5-(2 0 -ethyl-hexyloxy)-p-phenylene vinylene ) (MEH-PPV)-based hole-on ly diodes is investigated at high electric fields and low temperat ures using a novel diode architecture. Charge carrier densities that are in the range of those in a field-effect transistor are achieved, bridging the gap in the mobility versus charge carrier density plot between polymer-based light-emitting diodes and field-effect transistors. The extended field range that is accessed allows us to discuss the applicability of current theoretical models of charge transport, using numer ical simulations. Finally, within a simple approximation, we extract the hopping length for holes in MEH-PPV directly from the experimental data at high fields, and we derive a value of 1.0 ± 0.1 nm.
Dispersive Gaussian Hole Transport in a Molecularly Doped Polymer
2010
A common experimental technique used to measure charge transport in OPC’s is Time of Flight (TOF) [1]. The OPC is initially negatively charged so a capacitor with an applied uniform electric field is formed. A monochromatic short pulse of light is flashed upon the sample and creates electron-hole pairs which are pulled apart by the external field. Holes travel along the sample until they discharge the front electrode and thus produce a displacement current. By the signal shape and magnitude hole transport can be studied. A transient of rectangular shape is produced by a well-defined sheet of charge carriers moving at a constant velocity. The decay of an actual current, however, shows rounded fall-off near tτ, the carrier transit time, due to normal (Gaussian) diffusion superimposed on the field-induced drift. For some amorphous semiconductors [2] the current decreases continuously, and its flow extends to very long times so that in a double logarithmic scale it will show two slopes ...
On the field and temperature dependence of hole mobility in molecularly doped polymer
Synthetic Metals, 2005
The charge transport properties of N,N-diphenyl-N,N-bis(3-methylphenyl)-(1,1-biphenyl)-4,4-diamine (TPD) doped polycarbonate (PC) have been measured as a function of field and temperature. Hole mobility is observed to follow log µ ∝ E 1/2 (i.e. Poole-Frenkel behavior) at relatively high field strengths while at low field strengths mobility initially decreased with increase in field strength. Mobility value undergoes minima at a particular field value for a given temperature. Minima in mobility are observed to occur at higher field strength as the temperature is lowered. Mobility data and transport parameters are analyzed using the formalism of Gaussian disorder model (GDM). The mobility behavior at low field and shift of mobility minima with temperature suggests large disorder in the film. Investigation of film morphology using photoluminescence, X-ray diffraction and scanning electron microscopy suggests that large positional disorder in the film is probably due to film morphology and TPD-PC interaction.
Investigation of hole-mobility in a polyfluorene copolymer by admittance spectroscopy
Applied Physics Letters, 2010
Transport of holes in a low band gap polyfluorene, APFO-Green6, was investigated by means of admittance spectroscopy in the modulation frequency range 1 -10 6 Hz. At room temperature, hole mobility of APFO-Green6 is dependent on the applied electric field, as commonly observed in disordered organic materials. The excess capacitance toward low frequencies provides evidence for charge relaxation in trap levels. A dispersion parameter of 0.4 was achieved from the trend of hole transit times with the electric field.
Hole-transport properties of a low-band gap alternating polyfluorene
Journal of Applied Physics, 2010
The bulk transport properties of positive carriers in thin films of a low band-gap conjugated polymer, called APFO-Green5, have been investigated in the ac regime. The frequency-dependent impedance of an ITO/PEDOT:PSS/APFO-Green5/Al structure ͑where ITO is indium tin oxide and PEDOT:PSS is poly͑3,4-ethylenedioxythiophene͒/polystyrene sulphonic acid͒ was measured as a function of the dc applied bias. The capacitance response at low frequency gave indication of a combination of trapping and double-injection effects, while in the intermediate-high frequency range was determined by the transit time of injected holes. Hole mobility in APFO-Green5 thin films exhibited a Frenkel-like dependence on the applied electric field, with a field-dependent coefficient of around 8 ϫ 10 −3 ͑V cm −1 ͒ −1/2 . A hole mobility close to 2 ϫ 10 −5 cm 2 V −1 s −1 was achieved at the field of 3.5ϫ 10 5 V cm −1 , in excellent agreement with that already reported by using a different bulk investigation technique.